Evaporative Emissions System: Description and Operation
- The evaporative emission control system is employed to prevent evaporative fuel from being discharged into ambient atmosphere. This system includes a canister, purge control solenoid valve, fuel cut valve, their connecting lines, etc.
- Gasoline vapor evaporated from the fuel in the fuel tank is introduced into the canister through the evaporation line, and is absorbed on activated carbon in it. A Fuel cut valve is also incorporated on the fuel tank line.
- The purge control solenoid valve is controlled by the ECM and provides optimal purge control according to the engine condition. The signal from the fuel temperature sensor and fuel level sensor installed in the fuel tank is also used for this control.
- A pressure control solenoid valve incorporated in the fuel tank evaporation line controls the pressure/vacuum in the fuel tank according to the pressure/vacuum sensed by the fuel tank pressure sensor.
FUEL CUT VALVE
On AWD model, the fuel cut valve is built onto the evaporation pipe of the fuel tank cap. The rising level of the fuel from the fuel tank causes the float to move up and close the cap hole so that no fuel can enter during evaporation line.
FUEL CAP
The relief valve is adopted to prevent the development of vacuum in the fuel tank which may occur in case of trouble in the fuel vapor line.
In normal condition, the filler pipe is sealed at (A) and at the packing pressed against the filler pipe end. As vacuum develops in the fuel tank, atmospheric pressure forces the spring down to open the valve; consequently air is led into the fuel tank controlling the inside pressure.
CANISTER
The canister temporarily stores the evaporation gas. When the purge control solenoid valve is opened from a signal sent from the ECM, the evaporation gas is sent into the collector chamber after being mixed with fresh external air.
PURGE CONTROL SOLENOID VALVE
The purge control solenoid valve is on the evaporation line between canister and throttle body. It is installed at the under side of intake manifold.
TWO-WAY VALVE
- The two-way valve is located in the evaporation line between the fuel tank and canister. When evaporation gas pressure in fuel tank exceeds the specified value, the valve is pressurized to push the spring. This lifts the valve seat so that evaporative gas is discharged to the canister.
- When evaporation gas pressure in fuel tank drops specified value, the valve move to close the valve seat. However, air which enters from the inlet port of the canister is introduced into the fuel tank through the pin hole located at end of the valve.
PRESSURE CONTROL SOLENOID VALVE
The fuel tank pressure control solenoid valve located in the evaporation line between the fuel tank and the canister adjusts the pressure inside the fuel tank under the control of ECM.
- While the engine is running, ECM detects the evaporation gas pressure in the fuel tank through the signal from the fuel tank pressure sensor installed at the fuel filler pipe.
When the evaporation gas pressure in the fuel tank exceeds the specified value, ECM moves up/down the fuel tank pressure control solenoid valve plunger to open/close the control valve.
- During the engine stop, the fuel tank pressure control solenoid valve works as a two-way valve. (Two-way valve operation is the same as that used in other models.)
When the evaporation gas pressure in the fuel tank exceeds the specified value, it overcomes the valve spring force and opens the valve, and the gas is lead to the canister.
When the evaporation gas pressure in the fuel tank drops under the specified value, the valve closes. When the pressure lowers further, air from the inlet port of the canister is introduced into the fuel tank through the pin hole at the end of the valve.
VENT CONTROL SOLENOID VALVE
The vent control solenoid valve is installed at the intake port of the canister which opens to the atmosphere.
Normally, the valve is opened and the atmosphere is taken in the canister.
On the inspection of the evaporation gas leak at the evaporation line, this valve receives a signal from ECM and moves the shaft to the right to close the intake port of the canister.
AIR FILTER
The air filter is installed at the air inlet port of the vent control solenoid valve to clean the air taken in the canister through the vent control solenoid valve.